In the course of drilling and producing oil and gas wells it has been found be beneficial to keep the tubular, which may be drill pipe, casing, production pipe, or screens generally centered in the well. In certain instances it may be desirable to center one tubular within another. By keeping the tubular generally centered in the well a substantially uniform annular area between the wellbore wall and the tubular is maintained. In certain instances, such as cementing the tubular into the well, centralization to provide a substantially uniform annular area is imperative. By having a substantially uniform annular area the cement is better able to fill all voids between the tubular and the well thereby forming a better bond with both the wellbore wall and the tubular.
A common type of centralizer is a bow spring centralizer. A bow spring centralizer typically includes a number of bows attached to a collar on the upper end of the bow and on the lower end of the bow. The bow typically curves radially outward between the two collars. In its simplest form the bow spring centralizer slides over a tubular joint and is restricted only by the tubular couplings at either end of the tubular joint. In some situations, when the bow spring centralizer is pushed into a wellbore on a tubular string the leading collar may be stopped by a restriction that will cause the bows to longitudinally compress thereby radially expanding the bows radially outwards ultimately causing the bow to fail as the tubular string continues to move down into the well. The problem is compounded due to the thickness of the bow spring centralizer's collars and ribs. Usually the collars and the ribs had the same thickness however the thickness of the centralizer as a whole centralizer was effectively doubled because the ribs were welded on top of the collar. In the event that a rib was welded edge to edge to the collar a generally weaker collar to rib interface is created and stress points are created by both the welding process and the remaining corners or other sharp points.
One solution has been to attach at least one of the collars of the bow spring centralizer so that the centralizer will be pulled into the wellbore rather than pushed into the wellbore.